Slurry for thermal spraying, thermal spray coating, and method for forming thermal spray coating

ABSTRACT

A thermal spray slurry of the present invention contains ceramic particles in a content of 10% by mass or more and 85% by mass or less, and has a viscosity of 3,000 mPa·s or less. The ceramic particles have an average particle size of, for example, 1 nm or more and 5 μm or less. The thermal spray slurry may further contain a dispersant. The thermal spray slurry may further contain a viscosity modifier. The thermal spray slurry may further contain a flocculant.

TECHNICAL FIELD

The present invention relates to a thermal spray slurry containing ceramic particles, a thermal spray coating formed by using the thermal spray slurry, and a method for forming the thermal spray coating.

BACKGROUND ART

Ceramic thermal spray coatings are used in various applications according to the properties of the constituent ceramics. For example, aluminum oxide thermal spray coatings are used as protective coatings for various members because aluminum oxide exhibits high electric insulation, abrasion resistance, and corrosion resistance. Yttrium oxide thermal spray coatings are used as protective coatings for members in semiconductor device production apparatuses because yttrium oxide exhibits high plasma erosion resistance (see, for example, patent document 1 and patent document 2).

A ceramic thermal spray coating can be formed by thermally spraying a slurry containing ceramic particles (see, for example, patent document 3). However, there is a problem such that the thermal spraying of slurries is lower in thermal spraying efficiency as compared with the thermal spraying of powders. In order to improve the thermal spraying efficiency of the thermal spraying of a slurry, it is effective to increase the amount of the ceramic particles contained in the slurry. However, in such a case, the fluidity of the slurry is degraded, and consequently, it is sometimes difficult to form a thermal spray coating.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: Japanese Laid-Open Patent Publication No. 2002-80954 Patent document 2: Japanese Laid-Open Patent Publication No. 2006-144094 Patent document 3: Japanese Laid-Open Patent Publication No. 2010-150617

SUMMARY OF THE INVENTION Problems that are to be Solved by the Invention

Accordingly, an objective of the present invention is to provide a thermal spray slurry capable of satisfactorily forming a ceramic thermal spray coating. Another objective of the present invention is to provide a thermal spray coating formed by using the thermal spray slurry and a method for forming the thermal spray coating.

Means for Solving the Problem

In order to achieve the above-described objective and in accordance with an aspect of the present invention, a thermal spray slurry is provided that contains ceramic particles in a content of 10% by mass or more and 85% by mass or less, and has a viscosity of 3,000 mPa·s or less.

The ceramic particles have an average particle size of, for example, 1 nm or more and less than 200 nm. In this case, the thermal spray slurry may further contain a dispersant. Alternatively, or in addition to the dispersant, the thermal spray slurry may further contain a viscosity modifier.

The ceramic particles have an average particle size of, for example, 200 nm or more and 5 μm or less. In this case, the thermal spray slurry may further contain a flocculant.

In accordance with another aspect of the present invention, a thermal spray coating is provided that is obtained by thermally spraying the thermal spray slurry according to the above-described aspect.

In accordance with yet another aspect of the present invention, a method for forming a thermal spray coating is provided, wherein the thermal spray coating is formed by high velocity flame spraying of the thermal spray slurry according to the above-described aspect, containing water as a dispersion medium.

In accordance with still yet another aspect of the present invention, a method for forming a thermal spray coating is provided, wherein the thermal spray coating is formed by plasma spraying of the thermal spray slurry according to the above-described aspect, containing an organic solvent as a dispersion medium.

In the method of the above-described aspect, the thermal spray slurry may be fed to a thermal spraying apparatus by an axial feeding method. Alternatively, the thermal spray slurry may be fed to the thermal spraying apparatus by using two feeders in such a way that the variation period of the feed rate of the thermal spray slurry from one of the feeders is opposite in phase to that from the other feeder. Alternatively, the thermal spray slurry delivered from a feeder is temporarily stored in a tank immediately before reaching the thermal spraying apparatus, and the slurry in the tank may be fed to the thermal spraying apparatus by utilizing free fall of the thermal spray slurry. Alternatively, the thermal spray slurry may be fed to the thermal spraying apparatus through an electrically conductive tube. During the thermal spraying, the thermal spray slurry may be heated to a temperature of preferably 110% or more of the melting point of the ceramic particles.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a first embodiment of the present invention is described.

A thermal spray slurry is used, for example, to form a thermal spray coating. When the thermal spray slurry is thermally sprayed to a substrate, a thermal spray coating is formed on the substrate. With respect to the type of the substrate, it does not particularly matter whether the substrate is made of a metal, a ceramic, or any other material.

The thermal spray slurry is prepared by mixing ceramic particles in a dispersion medium, such as water and an organic solvent. The mixing may be performed by using a blade type stirrer, a homogenizer, or a mixer.

Examples of the organic solvent usable as the dispersion medium include alcohols, such as methanol, ethanol, n-propyl alcohol, and isopropyl alcohol, toluene, hexane, and kerosene. It is preferable to appropriately select the type of the dispersion medium used according to the thermal spraying method of the thermal spray slurry. Specifically, when the thermal spray slurry is thermally sprayed by high velocity flame spraying, it is preferable to use, as the dispersion medium, water, an organic solvent, or a mixture composed of water and an organic solvent. When the thermal spray slurry is plasma sprayed, it is preferable to use an organic solvent as a dispersion medium; however, it is also possible to use water or a mixture composed of water and an organic solvent in place of the organic solvent.

The ceramic particles contained in the thermal spray slurry may be particles made of an oxide ceramic, such as yttrium oxide, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, yttria-stabilized zirconium oxide, chromium oxide, zinc oxide, mullite, yttrium aluminum garnet (YAG), cordierite, and zircon. Alternatively, the ceramic particles may be particles made of a spinel ceramic; an oxide ceramic containing a rare earth element, such as scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); or a double oxide ceramic, containing aluminum (Al), silicon (Si), manganese (Mn), zinc (Zn), calcium (Ca), sodium (Na), phosphorus (P), fluorine (F), or boron (B). Alternatively, the ceramic particles may be particles made of a carbide ceramic, such as boron carbide.

The average particle size of the ceramic particles used is 1 nm or more and preferably 10 nm or more, and is less than 200 nm and preferably less than 150 nm. In this case, the ceramic particles are easily dispersed and stabilized in the thermal spray slurry.

The content of the ceramic particles in the thermal spray slurry, namely, the solid content concentration of the slurry is preferably 10% by mass or more, more preferably 20% by mass or more, and furthermore preferably 30% by mass or more. In this case, it is easy to improve the thickness of the thermal spray coating produced per unit time from the thermal spray slurry, namely, the thermal spraying efficiency.

The content of the ceramic particles in the thermal spray slurry is also preferably 85% by mass or less, more preferably 70% by mass or less, and furthermore preferably 50% by mass or less. In this case, it is easy to obtain a thermal spray slurry having a required fluidity appropriate for satisfactory feeding to a thermal spraying apparatus, namely, a thermal spray slurry having a required fluidity sufficient for forming a thermal spray coating.

The pH of the thermal spray slurry is preferably 6 or more, more preferably 7 or more, and furthermore preferably 8 or more. In this case, it is easy to improve the storage stability of the thermal spray slurry.

The pH of the thermal spray slurry is also preferably 11 or less, more preferably 10.5 or less, and furthermore preferably 10 or less. In this case, it is easy to improve the dispersion stability of the ceramic particles in the thermal spray slurry.

The absolute value of the zeta potential of the ceramic particles in the thermal spray slurry is preferably 10 mV or more, more preferably 25 mV or more, and furthermore preferably 40 mV or more. In this case, it is easy to improve the dispersion stability of the ceramic particles in the thermal spray slurry because the ceramic particles electrically and strongly repel each other.

The sedimentation velocity of the ceramic particles in the thermal spray slurry is preferably 50 μm/sec or less and more preferably 30 μm/sec or less. The sedimentation velocity can be used as an index for indicating the degree of the dispersion stability of the ceramic particles in the thermal spray slurry.

The viscosity of the thermal spray slurry is preferably 3,000 mPa·s or less, more preferably 1,000 mPa·s or less, furthermore preferably 500 mPa·s or less, and most preferably 100 mPa·s or less. With the decrease of the viscosity, it becomes easy to obtain a thermal spray slurry having a required fluidity sufficient for forming a thermal spray coating.

The thermal spray slurry may further contain a dispersant, if necessary. The dispersant as referred to herein means a compound capable of improving the dispersion stability of the ceramic particles in the thermal spray slurry. The dispersant may be anionic, cationic, or nonionic. Examples of the anionic dispersant include polycarboxylic acid dispersants, such as polycarboxylic acid sodium salt, polycarboxylic acid ammonium salt, and polycarboxylic acid polymer; naphthalenesulfonic acid dispersants, such as naphthalenesulfonic acid sodium salt and naphthalenesulfonic acid ammonium salt; alkylsulfonic acid dispersants; and polyphosphoric acid dispersants. Examples of the cationic dispersant include polyalkylene polyamine dispersants, quaternary ammonium dispersants, alkyl polyamine dispersants, and imidazoline dispersants, such as alkylimidazoline. Examples of the nonionic dispersant include alkylene oxide dispersants and polyhydric alcohol ester dispersants.

The thermal spray slurry may further contain a viscosity modifier, if necessary. The viscosity modifier as referred to herein means a compound capable of decreasing or increasing the viscosity of the thermal spray slurry. By appropriately regulating the viscosity of the thermal spray slurry, the decrease of the fluidity of the thermal spray slurry is suppressed even when the content of the ceramic particles in the thermal spray slurry is relatively high. Examples of the compound usable as the viscosity modifier include nonionic polymers; polyethers, such as polyethylene glycol; and cellulose derivatives, such as carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC).

The thermal spray slurry may further contain a defoaming agent, if necessary. The defoaming agent as referred to herein means a compound capable of preventing the formation of bubbles in the thermal spray slurry during the production or the thermal spraying of the thermal spray slurry, or a compound capable of vanishing bubbles formed in the thermal spray slurry. Examples of the defoaming agent include silicone oil, silicone emulsion defoaming agents, polyether defoaming agents, and fatty acid ester defoaming agents.

The thermal spray slurry may further contain an antiseptic or a fungicide, if necessary. Examples of the antiseptic or the fungicide include isothiazoline compounds, azole compounds, and propylene glycol.

When a dispersant, a viscosity modifier, a defoaming agent, an antiseptic, or a fungicide is used, during the preparation of the thermal spray slurry, the dispersant, the viscosity modifier, the defoaming agent, the antiseptic, or the fungicide may be added to the dispersion medium at the same timing as that of the addition of the ceramic particles, or at the timing different from that of the addition of the ceramic particles.

The method for thermally spraying the thermal spray slurry may be a high velocity flame spraying method, in which the thermal spray slurry is fed into the center of the high velocity combustion flame jet flow generated with high-pressure oxygen (or air) and a fuel and is continuously jetted at a high velocity, such as a high velocity oxygen fuel spraying method (HVOF). Alternatively, the method may be a plasma spraying method, in which the thermal spray slurry is fed into the center of the plasma jet flow generated from the gas in a plasma form and is jetted, such as an atmospheric-pressure plasma spraying method (APS). When the thermal spray slurry of the present invention is thermally sprayed by the high velocity flame spraying method or the plasma spraying method, the thermal spray slurry, high in the content of ceramic particles, can be thermally sprayed with a satisfactory fluidity, and a dense thermal spray coating can be formed efficiently.

When the thermal spray slurry contains water as the dispersion medium, it is preferable to use the high velocity flame spraying method. When the dispersion medium contained in the thermal spray slurry is an organic solvent, it is preferable to use the plasma spraying method. The fuel used in the high velocity flame spraying method may be a hydrocarbon gas fuel, such as acetylene, ethylene, propane, and propylene, or a liquid fuel, such as kerosene and ethanol.

The thermal spray slurry is heated during thermal spraying to a temperature of preferably 110% or more of the melting point of the ceramic particles. In this case, the ceramic particles are sufficiently heated during thermal spraying, and hence it becomes easy to obtain a dense thermal spray coating.

The thermal spraying distance, namely, the distance from the tip of the nozzle of the thermal spraying apparatus to the substrate is preferably 30 mm or more. In this case, it becomes easy to suppress thermal alteration or thermal deformation of the substrate.

The thermal spraying distance is also preferably 200 mm or less. In this case, the ceramic particles are sufficiently heated during thermal spraying, and hence it becomes easy to obtain a dense thermal spray coating.

It is preferable to perform the feeding of the thermal spray slurry to the thermal spraying apparatus by the axial feeding method, namely, to perform the feeding of the thermal spray slurry in the same direction as the axis of the jet flow generated in the thermal spraying apparatus. When the thermal spray slurry of the present invention is fed to the thermal spraying apparatus by the axial feeding method, attachment of the ceramic particles in the thermal spray slurry is less likely to occur inside the thermal spraying apparatus since the thermal spray slurry has good fluidity, and thus a dense thermal spray coating can be formed efficiently.

When the thermal spray slurry is fed to the thermal spraying apparatus by using a common feeder, a periodic variation of the feed rate occurs, and hence stable feeding of the slurry is difficult. The periodic variation of the feed rate is also referred to as pulsation. When the pulsation increases the feed rate of the thermal spray powder, the ceramic particles are less likely to be uniformly heated in the thermal spraying apparatus, and a nonuniform thermal spray coating is sometimes formed. Accordingly, in order to stably feed the thermal spray slurry to the thermal spraying apparatus, a two-stroke method may be adopted, namely, two feeders may be used in such a way that the variation period of the feed rate of the thermal spray slurry from one of the feeders is opposite in phase to that from the other feeder. Specifically, the feeding method may be regulated so as to have a period such that when the feed rate from one feeder is increased, the feed rate from the other feeder is decreased. When the thermal spray powder of the present invention is fed to the thermal spraying apparatus by the two-stroke method, a dense thermal spray coating can be formed efficiently since the thermal spray powder has good fluidity.

Means for stably feeding the thermal spray slurry to the thermal spraying apparatus are as follows. That is, a tank may be provided in which the thermal spray slurry delivered from the feeder is temporarily stored immediately before the slurry reaches the thermal spraying apparatus, and the thermal spray slurry in the tank may be fed to the thermal spraying apparatus by utilizing free fall of the slurry. Alternatively, the thermal spray slurry in the tank may be fed to the thermal spraying apparatus in a forcible manner by using a device such as a pump. When the slurry is fed in a forcible manner by using a device such as a pump, even in the case where the tank and the thermal spraying apparatus are connected with each other through a tube, attachment of the ceramic particles in the thermal spray slurry is less likely to occur inside the tube. In order to make uniform the distribution of the components in the thermal spray slurry stored in the tank, a device for stirring the thermal spray slurry in the tank may be provided.

The feeding of the thermal spray slurry to the thermal spraying apparatus is performed preferably through an electrically conductive tube made of, for example, a metal. When an electrically conductive tube is used, the occurrence of static electricity is suppressed, and hence the variation of the feed rate of the thermal spray slurry is less likely to occur. The inner surface of the electrically conductive tube has a surface roughness Ra of preferably 0.2 μm or less.

Next, a second embodiment of the present invention is described by focusing on the differences from the first embodiment.

A thermal spray slurry of the second embodiment is different from the thermal spray slurry of the first embodiment in that the average particle size of the ceramic particles used is 200 nm or more and preferably 500 nm or more, and 5 μm or less and preferably 4 μm or less. Since the thermal spray slurry of the second embodiment contains ceramic particles having a relatively large particle size as described above, the ceramic particles are easily sedimented by gravity in the thermal spray slurry to produce precipitates. Accordingly, when the thermal spray slurry of the second embodiment is used, an operation such as stirring for redispersing the precipitated ceramic particles is required.

The thermal spray slurry of the second embodiment may further contain a flocculant, if necessary. The flocculant as referred to herein means a compound capable of flocculating the ceramic particles in the thermal spray slurry. When a flocculant is contained in the thermal spray slurry, precipitates of the ceramic particles are formed in a state such that the flocculant is interposed between the ceramic particles, and hence the redispersibility of the precipitated ceramic particles is improved. Specifically, the precipitated ceramic particles are easily redispersed by an operation such as stirring, and hence the operation for the redispersion becomes simple. The flocculant may be any of an aluminum flocculant, an iron flocculant, a polymer flocculant, and an organic compound flocculant. Examples of the aluminum flocculant include aluminum sulfate (also referred to as alum), aluminum chloride, and polyaluminum chloride (also referred to as PAC or PACT). Examples of the iron flocculant include ferric chloride and polyferric sulfate. Examples of the polymer flocculant include isobutylene-maleic acid copolymer and carboxy vinyl polymer. The polymer flocculant may be any of an anionic polymer flocculant, a cationic polymer flocculant, and a nonionic polymer flocculant. Examples of the organic compound flocculant include organic acids, such as malic acid, succinic acid, citric acid, maleic acid, and maleic anhydride.

When a flocculant is used, during the preparation of the thermal spray slurry, the flocculant may be added to the dispersion medium at the same timing as that of the addition of the ceramic particles, or at the timing different from that of the addition of the ceramic particles.

(Operation)

Since the above-described thermal spray slurry of each of the first and second embodiments has a content of the ceramic particle of 85% by mass or less and a viscosity of 3,000 mPa·s or less, the slurry can have a required fluidity suitable for satisfactory feeding to the thermal spraying apparatus even when the content of the ceramic particles in the thermal spray slurry is relatively high. In other words, the thermal spray slurry of each of the first and second embodiments can each have a required fluidity sufficient for forming a thermal spray coating. Moreover, the content of the ceramic particles in each of the thermal spray slurries is 10% by mass or more, and hence each of the thermal spray slurries can ensure a required thermal spraying efficiency.

Advantageous Effects

Accordingly, according to each of the first and second embodiments, a thermal spray slurry is provided that is capable of satisfactorily forming a ceramic thermal spray coating.

(Modifications)

The first and second embodiments may be modified as follows.

-   -   The ceramic particles in the thermal spray slurry may contain a         component or components other than ceramics.     -   The thermal spray slurry may contain two or more types of         ceramic particles.     -   The thermal spray slurry of the first embodiment may contain two         or more types of dispersants.     -   The thermal spray slurry of the first embodiment may contain two         or more types of viscosity modifiers.     -   The thermal spray slurry may contain two or more types of         defoaming agents.     -   The thermal spray slurry may contain two or more types of         antiseptics.     -   The thermal spray slurry may contain two or more types of         fungicides.     -   The thermal spray slurry of the first embodiment may contain a         flocculant.     -   The thermal spray slurry of the second embodiment may contain         two or more types of flocculants.     -   The thermal spray slurry of the second embodiment may contain a         dispersant, a viscosity modifier, a defoaming agent, an         antiseptic, or a fungicide.     -   The thermal spray slurry may contain two or more of a         dispersant, a viscosity modifier, a defoaming agent, an         antiseptic, a fungicide, and a flocculant.     -   The thermal spray slurry may further contain a component or         components other than a dispersant, a viscosity modifier, a         defoaming agent, an antiseptic, a fungicide, and a flocculant.     -   The components other than the dispersion medium in the thermal         spray slurry are prepared as contained in one or more packages         other than the package for the dispersion medium, and the         thermal spray slurry may be prepared by mixing the components         other than the dispersion medium with the dispersion medium. In         this case, the thermal spray slurry can be simply prepared even         immediately before thermal spraying.

Examples

Next, the present invention is described more specifically with reference to examples and comparative examples.

In each of Examples 1 to 42 and Comparative Examples 1 to 3, a thermal spray slurry was prepared by mixing ceramic particles with a dispersion medium, and by further mixing with the resulting mixture a dispersant, a viscosity modifier, or a flocculant, if necessary. The details of each of the thermal spray slurries are shown in Table 1.

TABLE 1 Average Content particle of Deposi- size of ceramic tion Deposition Type of ceramic ceramic particles Viscosity Viscosity Sedimentation property property Dispersion medium particles particles (% by mass) Dispersant modifier Flocculant (mPa · s) property (1) (2) Comparative Water Al₂O₃  12 nm 5 — — Isobutylene- 393 No sedimentation x x Example 1 maleic acid copolymer Example 1 Water Al₂O₃  12 nm 25 — — Isobutylene- 2800 No sedimentation — ∘ maleic acid copolymer Example 2 Ethanol Al₂O₃  12 nm 25 — PEG — 2721 No sedimentation ∘ ∘ Example 3 Ethanol Y₂O₃  12 nm 20 — PEG — 2534 No sedimentation ∘ ∘ Example 4 Ethanol YSZ  12 nm 25 — PEG — 2830 No sedimentation ∘ ∘ Example 5 Water Al₂O₃ 1.2 μm 40 — — Isobutylene- 225 Sedimentation — ∘ maleic acid copolymer Example 6 Water Al₂O₃ 1.2 μm 40 — PEG — 199 Sedimentation — ∘ Example 7 Water Al₂O₃ 4.4 μm 40 — PEG — 147 Sedimentation — ∘ Example 8 Mixture of water Al₂O₃ 1.2 μm 40 — PEG — 244 Sedimentation ∘ ∘ and ethanol Example 9 Water Al₂O₃ 1.2 μm 40 — — Aluminum 163 Sedimentation — ∘ sulfate Example 10 Water Al₂O₃ 1.2 μm 40 Polyalkylene polyamine — — 172 Sedimentation — ∘ Example 11 Ethanol Al₂O₃ 1.2 μm 70 — — Isobutylene- 621 Sedimentation ∘ ∘ maleic acid copolymer Example 12 Ethanol Y₂O₃ 1.2 μm 70 — — Isobutylene- 933 Sedimentation ∘ ∘ maleic acid copolymer Example 13 Ethanol YSZ 1.2 μm 70 — — Isobutylene- 719 Sedimentation ∘ ∘ maleic acid copolymer Example 14 Ethanol Al₂O₃ 1.2 μm 70 — PEG Isobutylene- 577 Sedimentation ∘ ∘ maleic acid copolymer Comparative Water Al₂O₃ 1.2 μm 70 — — — 8800 Sedimentation — x Example 2 Comparative Water Al₂O₃ 1.2 μm 90 — — — Unmeasurable Sedimentation — x Example 3 Example 15 Water Y₂O₃ 0.6 μm 35 Sodium polycarboxylate — — 225 Sedimentation — ∘ Example 16 Water Y₂O₃ 1.6 μm 25 Sodium polycarboxylate — — 2 Sedimentation — ∘ Example 17 Water Y₂O₃ 1.6 μm 35 Sodium polycarboxylate — — 5 Sedimentation — ∘ Example 18 Water Y₂O₃ 1.6 μm 50 Sodium polycarboxylate — — 7 Sedimentation — ∘ Example 19 Water Y₂O₃ 0.6 μm 35 Ammonium polycarboxylate — — 225 Sedimentation — ∘ Example 20 Water Y₂O₃ 1.6 μm 25 Ammonium polycarboxylate — — 2 Sedimentation — ∘ Example 21 Water Y₂O₃ 1.6 μm 35 Ammonium polycarboxylate — — 5 Sedimentation — ∘ Example 22 Water Y₂O₃ 1.6 μm 50 Ammonium polycarboxylate — — 7 Sedimentation — ∘ Example 23 Water Y₂O₃ 1.6 μm 35 Polycarboxylic acid polymer — — 8 Sedimentation — ∘ Example 24 Water Y₂O₃ 1.6 μm 30 Sodium — Carboxy vinyl 5 Sedimentation — ∘ polycarboxylate polymer Example 25 Water Y₂O₃ 1.6 μm 30 Ammonium — Carboxy vinyl 5 Sedimentation — ∘ polycarboxylate polymer Example 26 Mixture of ethanol, Y₂O₃ 2.6 μm 10 Sodium — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 27 Mixture of ethanol, Y₂O₃ 2.6 μm 10 Ammonium — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 28 Mixture of ethanol, Y₂O₃ 1.6 μm 30 Alkylimidazoline — — 2 Sedimentation ∘ ∘ isopropyl alcohol, and normal propyl alcohol Example 29 Mixture of ethanol, Y₂O₃ 2.6 μm 30 Alkylimidazoline — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and normal propyl alcohol Example 30 Mixture of ethanol, Y₂O₃   6 μm 30 Alkylimidazoline — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and normal propyl alcohol Example 31 Mixture of ethanol, Y₂O₃ 1.6 μm 30 Alkylimidazoline — Carboxy vinyl 20 Sedimentation ∘ ∘ isopropyl alcohol, and polymer normal propyl alcohol Example 32 Mixture of ethanol, Y₂O₃   6 μm 30 Alkylimidazoline — Carboxy vinyl 20 Sedimentation ∘ ∘ isopropyl alcohol, and polymer normal propyl alcohol Example 33 Mixture of ethanol, Al₂O₃ 1.1 μm 10 Sodium — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 34 Mixture of ethanol, Al₂O₃ 1.1 μm 10 Ammonium — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 35 Water (La—Yb—Al—Si—Zn)O 1.6 μm 30 Sodium — — 2 Sedimentation — ∘ polycarboxylate Example 36 Mixture of ethanol, (La—Yb—Al—Si—Zn)O 1.6 μm 30 Sodium — — 2 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 37 Water (La—Yb—Al—Si—Zn)O 1.6 μm 30 Ammonium — — 2 Sedimentation — ∘ polycarboxylate Example 38 Mixture of ethanol, (La—Yb—Al—Si—Zn)O 1.6 μm 30 Ammonium — — 2 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 39 Water (La—Al—Si—Ca—Na—P—F—B)O 4.8 μm 30 Sodium — — 1 Sedimentation — ∘ polycarboxylate Example 40 Mixture of ethanol, (La—Al—Si—Ca—Na—P—F—B)O 4.8 μm 30 Sodium — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol Example 41 Water (La—Al—Si—Ca—Na—P—F—B)O 4.8 μm 30 Ammonium — — 1 Sedimentation — ∘ polycarboxylate Example 42 Mixture of ethanol, (La—Al—Si—Ca—Na—P—F—B)O 4.8 μm 30 Ammonium — — 1 Sedimentation ∘ ∘ isopropyl alcohol, and polycarboxylate normal propyl alcohol

The column “Dispersion medium” in Table 1 shows the type of the dispersion medium used in each of the thermal spray slurries.

The column “Type of ceramic particles” in Table 1 shows the type of the ceramic particles used in each of the thermal spray slurries. In the same column, “Al₂O₃” represents aluminum oxide, “Y₂O₃” represents yttrium oxide, “YSZ” represents yttria-stabilized zirconium oxide, “(La—Yb—Al—Si—Zn)O” represents a double oxide ceramic containing lanthanum, ytterbium, aluminum, silicon, and zinc, and “(La—Al—Si—Ca—Na—P—F—B)O” represents a double oxide ceramic containing lanthanum, aluminum, silicon, calcium, sodium, phosphorus, fluorine, and boron.

The column “Average particle size of ceramic particles” in Table 1 shows the average particle size of the ceramic particles used in each of the thermal spray slurries. The average particle size was calculated from the specific surface areas of the ceramic particles measured by using the specific surface area measurement apparatus “Flow Sorb II 2300” manufactured by Micromeritics Corp.

The column “Content of ceramic particles” in Table 1 shows the content of the ceramic particles in each of the thermal spray slurries.

The column “Dispersant” in Table 1 shows the type of the dispersant used in each of the thermal spray slurries. In the same column, the hyphen (-) indicates no use of a dispersant. When a dispersant was used, the dispersant was used in an amount to give a content of 2% by mass of the dispersant in the thermal spray slurry.

The column “Viscosity modifier” in Table 1 shows the type of the viscosity modifier used in each of the thermal spray slurries. In the same column, “PEG” represents polyethylene glycol, and the hyphen (-) indicates no use of a viscosity modifier. When a viscosity modifier was used, the viscosity modifier was used in an amount to give a content of 2% by mass of the viscosity modifier in the thermal spray slurry.

The column “Flocculant” in Table 1 shows the type of the flocculant used in each of the thermal spray slurries. In the same column, the hyphen (-) indicates no use of a flocculant. When a flocculant was used, the flocculant was used in an amount to give a content of 2% by mass of the flocculant in the thermal spray slurry.

The column “Viscosity” in Table 1 shows the measurement result of the viscosity of each of the thermal spray slurries at room temperature by using Viscotester VT-03F manufactured by RION Co., Ltd.

The column “Sedimentation property” in Table 1 shows the result of evaluating whether or not precipitates were formed when 700 mL of each of the thermal spray slurries was placed in a 16.5 cm-high vessel having a volume of 1 L, and was allowed to stand still at room temperature for 1 week. In the same column, “No sedimentation” represents the case where no precipitates were formed, and “Sedimentation” represents the case where precipitates were formed.

The column “Deposition property (1)” in Table 1 shows the result of evaluating whether or not a thermal spray coating was able to be obtained when each of the thermal spray slurries was atmospheric plasma sprayed under the conditions described in Table 2. In the same column, “o (good)” represents the case where the thickness of the thermal spray coating formed per one pass was 0.5 μm or more, “x (poor)” represents the case where the thickness concerned was less than 0.5 μm or the feeding of the thermal spray slurry was not able to be performed, and “−” represents the case where the test was not performed. It is to be noted that one pass means one time of thermal spraying operation performed by the thermal spraying apparatus (thermal spraying gun) along the traveling direction of the thermal spraying apparatus or the object of the thermal spraying (substrate).

The column “Deposition property (2)” in Table 1 shows the result of evaluating whether or not a thermal spray coating was able to be obtained when each of the thermal spray slurries was HVOF sprayed under the conditions described in Table 3. In the same column, “o (good)” represents the case where the thickness of the thermal spray coating formed per one pass was 2 μm or more, and “x (poor)” represents the case where the thickness concerned was less than 2 μm or the feeding of the thermal spray slurry was not able to be performed.

TABLE 2 Thermal spraying apparatus: “Axial III” manufactured by Northwest Mettech Corp. Slurry feeder: “M650” manufactured by Northwest Mettech Corp. Ar gas flow rate: 81 L/min Nitrogen gas flow rate: 81 L/min Hydrogen gas flow rate: 18 L/min Plasma power: 88 kW Thermal spraying distance: 50 mm Traveling speed of thermal spraying apparatus: 240 m/min Feed rate of thermal spray slurry: 3 L/hour

TABLE 3 Thermal spraying apparatus: “Top gun” manufactured by GTV GmbH Slurry feeder: Manufactured by GTV GmbH Acetylene gas flow rate: 75 L/min Oxygen gas flow rate: 230 L/min Thermal spraying distance: 90 mm Traveling speed of thermal spraying apparatus: 100 m/min Feed rate of thermal spray slurry: 4.5 L/hour

As shown in Table 1, in the case of the thermal spray slurry of each of Examples 1 to 42, the both evaluation results regarding the deposition properties were good. Although not shown in Table 1, the thermal spray coating obtained from the thermal spray slurry of each of Examples 1 to 42 was high in the degree of denseness in such a way that the porosity was 10% or less. 

1. A thermal spray slurry comprising ceramic particles in a content of 10% by mass or more and 85% by mass or less, and having a viscosity of 3,000 mPa·s or less.
 2. The thermal spray slurry according to claim 1, wherein the ceramic particles have an average particle size of 1 nm or more and less than 200 nm.
 3. The thermal spray slurry according to claim 2, further comprising a dispersant.
 4. The thermal spray slurry according to claim 2, further comprising a viscosity modifier.
 5. The thermal spray slurry according to claim 1, wherein the ceramic particles have an average particle size of 200 nm or more and 5 μm or less.
 6. The thermal spray slurry according to claim 5, further comprising a flocculant.
 7. A thermal spray coating obtained by thermally spraying the thermal spray slurry according to claim
 1. 8. A method for forming a thermal spray coating, comprising high velocity flame spraying the thermal spray slurry according to claim 1, containing water as a dispersion medium, to form a thermal spray coating.
 9. A method for forming a thermal spray coating, comprising plasma spraying the thermal spray slurry according to claim 1, containing an organic solvent as a dispersion medium, to form a thermal spray coating.
 10. The method for forming a thermal spray coating according to claim 8, further comprising feeding the thermal spray slurry to a thermal spraying apparatus by an axial feeding method.
 11. The method for forming a thermal spray coating according to claim 8, further comprising feeding the thermal spray slurry to a thermal spraying apparatus by using two feeders in such a way that the variation period of the feed rate of the thermal spray slurry from one of the feeders is opposite in phase to that from the other feeder.
 12. The method for forming a thermal spray coating according to claim 8, further comprising: temporarily storing the thermal spray slurry delivered from a feeder in a tank immediately before reaching a thermal spraying apparatus; and feeding the thermal spray slurry in the tank to the thermal spraying apparatus by utilizing free fall of the thermal spray slurry.
 13. The method for forming a thermal spray coating according to claim 8, further comprising feeding the thermal spray slurry to a thermal spraying apparatus through an electrically conductive tube.
 14. The method for forming a thermal spray coating according to claim 8, further comprising heating, during said spraying, the thermal spray slurry to a temperature of 110% or more of the melting point of the ceramic particles.
 15. The thermal spray slurry according to claim 3, further comprising a viscosity modifier.
 16. The method for forming a thermal spray coating according to claim 9, further comprising feeding the thermal spray slurry to a thermal spraying apparatus by an axial feeding method.
 17. The method for forming a thermal spray coating according to claim 9, further comprising feeding the thermal spray slurry to a thermal spraying apparatus by using two feeders in such a way that the variation period of the feed rate of the thermal spray slurry from one of the feeders is opposite in phase to that from the other feeder.
 18. The method for forming a thermal spray coating according to claim 9, further comprising: temporarily storing the thermal spray slurry delivered from a feeder in a tank immediately before reaching a thermal spraying apparatus; and feeding the thermal spray slurry in the tank to the thermal spraying apparatus by utilizing free fall of the thermal spraying slurry.
 19. The method for forming a thermal spray coating according to claim 9, further comprising feeding the thermal spray slurry to a thermal spraying apparatus through an electrically conductive tube.
 20. The method for forming a thermal spray coating according to claim 9, further comprising heating, during said spraying, the thermal spray slurry to a temperature of 110% or more of the melting point of the ceramic particles. 